PROJECT SUMMARY The levels of dietary methyl donors vary widely in the population and impact numerous cancer-related pathways. However, the role of folate and other methyl donors in the etiology of colon cancer is complex and controversial. We recently reported that dietary methyl donor depletion (MDD) affords dramatic protection against intestinal tumor formation in several Apc mouse cancer models, even after mice are returned to a normal methyl donor replete diet. Our current data suggest that epigenetic reprogramming contributes to this dramatic and durable cancer protection. Among the metabolic changes we observed were dramatic increases in the levels of the DNMT inhibitor, SAH, reducing DNA methylation among a panel of cancer-related genes, including Wnt targets. In response to PQ11, we will evaluate the possibility that a methyl donor restricted diet, when combined with standard FOLFOX chemotherapy, will enhance tumor cell killing and enable a durable and lasting protection to the colon, in part by preventing epigenetic-driven drug resistance. For our pre-clinical model, we will use the conditional Lrig1xApc mouse, in which distal colon tumors are induced by tamoxifen. The distribution of the tumors in this model to the distal colon will enable us to track their response to treatment in real-time using our mouse colonoscopy system. Overall, the proposed studies will help to elucidate the interplay between dietary methyl donors and colon cancer therapy. The extent to which cancer cell killing is enhanced by methyl donor restriction following FOLFOX administration will be determined. In addition, the possibility that methyl donor restriction affects epigenetic changes and gene expression patterns for long-lasting tumor suppression will be explored. We hypothesize that MDD causes gene-specific changes to DNA methylation and that sustained tumor protection results in part from lasting changes to the epigenome of cancer stem cells. This exploratory proposal could establish a novel paradigm for a nutritional intervention during colon cancer therapy to improve response rates and prevent the development of treatment-resistant cancers.